97 tahoe trans, transfer case, diff oils?

[Joey198705]

97 tahoe auto 350 push button 4 wheel drive. With about 180000 miles. Wanting to change they oil in the trans, transfer case, and rear end. Looking to see what everyone else uses or recommends

 

[willxfs]

I think there's a TSB that states the transfer case with the push button 4wd and auto feature must use the GM AutoTrac II fluid. Its blue in color. My manual states Dex III fluid but the TSB updates this. I had a shop, actually two shops put regular ATF in mine and it did ok for many miles. I finally changed it myself and used the AutoTrac II fluid. Transmission uses Dex III, I believe. I use the Valvoline Max Life full synthetic for the transmission. Been happy with that. I cant recall what the front and rear differentials use but I think it's recommended that full synthetic be used in one or the other. Probably the rear, for the G80, locking differential. No additives. But verify that info.

 

[alpinecrick]

Transmission: Dex III, all five of my 4L60E's currently have a mix of conventional and synthetic oil in them. Your trans holds roughly 12 quarts. Dropping the pan and changing the filter drains approximately 3 quarts. A tutorial to change out most of the oil: https://www.silveradosierra.com/how...-complete-fluid-changeover-filter-t14477.html

Transfer case:
Auto-Trak (Suburbans and Tahoes, Auto-Trak appeared in '97 on up....I think) The blue GM Auto-Trak II fluid.
Manual shift and Push button 4wd. Dex III (All pickups and 96 and earlier Suburbans and Tahoes, although some of the base Suburban/Tahoes may have used push button 4wd in later years).
In other words, anything with Auto-Trak requires GM blue fluid. Anything with manual or push-button 4wd requires Dex III. There is allegedly a bulletin that recommends only Dex III conventional fluid rather than synthetic. I've been running synthetic Dex III in my '96 pickup for the past 85,000 miles, and 30-40K in my '97 pickup before I ever heard about this.

Diffs: Your manual says 80-90w gear oil. Because the thermal actuators were prone to burn out--especially in cold weather--there was a bulletin that recommended switching to 75-90w synthetic in the front diff. I run 75-90w in both diffs in my GMT 400's and GMT 800.
My '01 Siverado's manual calls for 75-90w in the front diff, and the '99 GMT 400's apparently had synthetic installed at the factory in the front diffs.
In other words, the switch to synthetic 75-90 in the front diff was about the thermal actuator rather than lubrication.

 

[Sean James]

What others have said.

Mobil1 full synthetic 5-20 in crankcase. But use what you want, your an American.

For the trans, Valvoline Max-life full synthetic (Dex III and VI compatible), it's the best bang for the buck and available almost everywhere.

I've dropped transpan, installed cheap trans drain-plug kit from o'reillys with no leaks, works great, but I ditched the nylon washers and got a 2-pack of copper washers from the same section as the drain plug kit, no leaks whatsoever, $10. I add the 3 or so quarts of Valvoline Max-life full synthetic, to replace the old fluid (actually add 2 qts, check level and top off, drive till warm, and double check).

With high mileage, and unknown trans maintenance, I've read dozens of posts that said it's better to change fluid SLOWLY over time, mixing the new with the old. So add the 3 qts synthetic after the pan drop, drive it for a month. Then if you have installed the drain plug, drain out another 3 qts, and repeat for a few months. This should slowly give you all new fully synthetic trans fluid. I've had no issues doing it this way at all.

But if you install the drain plug, I would recommend using the 1/2" copper washers after you drill out the 1/2" hole for the drain plug, then clean up the edges of the hole in the pan, and use red loctite on the drain plug threads and torque it down real tight, and clean off ANY excess loctite from the assembly. (Do Not loctite the actual drain plug, but the nut and through-bolt that the plug goes into). Also, be very careful where you install the drain plug. It sits a little over 1/2" high in the pan, and if you don't install it (drill the hole) in the right place, the plug will hit the valve body and it won't go back together.

I put a large "test" nut in the pan that was a little taller than the drain plug, slapped some grease on the bottom to hold it in place, and then crawled under and checked for clearance in multiple spots. I believe I put it near the drivers side rear of pan, or maybe front, I was upside down on my back, so I don't remember, but you get the idea.

I've done this to all my trucks after I had one shatter the trans sun shell at 170K, and I never want that to happen again. I've also added larger external trans coolers to both trucks.

"Auto" 4wd with the 4 push buttons gets GM AutoTrak II ONLY! Takes almost exactly 2 qts. and it IS bright blue fluid! $10 a quart at NAPA, you should only need 2 qts unless you drain it on an uphill slope. Factory drain and fill plugs on rear of transfer case, fill to top of upper plug and done. I did put teflon tape on the plug threads, but only on the outer side, takes about 30 mins if you have a cheap bottle pump (which you will need unless you are VERY creative)

Front and rear diffs get Mobil1 75-90 full synthetic LS (limited slip) and a fel-pro gasket. The Mobil1 synthetic works just fine for non Limited Slip diffs.

And don't forget your radiator fluid, and brake fluid too. Brake reservoir fluid removed with syringe until ALMOST empty (dont uncover intake ports) and new DOT 4 or 6, 6 is backwards compatible.